This invention relates to laminated plastic molded bodies having extremely high gas barrier properties against oxygen and carbon dioxide gases, being transparent, having excellent mechanical properties and having food hygiene properties.
Various kinds of plastic containers have been on the market as a container for, for example, foods, drinks, cosmetics, chemicals or the like, since they have a light weight, a less danger of breakage, a low cost and the like. In particular, plastic containers made of poly(ethylene terephthalate) resins have an excellent transparency and show a beautiful appearance similar to glass bottles, so that they have been generally used as a container for drinks.
The above-mentioned plastic molded bodies made of the poly(ethylene terephthalate) resins are insufficient in the gas barrier properties against oxygen and carbon dioxide gases. Thus, by making a laminated plastic molded body in which the poly(ethylene terephthalate) resin layer and the other thermoplastic gas barrier resin layer are laminated, the body can be made suitable for its contents which require gas barrier properties.
However, lamination of the thermoplastic gas barrier resin layer causes problems of lowering in mechanical properties and lowering in transparency, so that a film thickness of the gas barrier resin layer to be laminated is inherently limited. Thus, with regard to its contents to be contained which require particularly excellent gas barrier properties, it is the present status that there is still a problem in its shelf life.
Thus, with regard to the conventional laminated plastic body in which the above-mentioned poly(ethylene terephthalate) resin layer and the thermoplastic gas barrier resin layer are laminated, the portion corresponding to the poly(ethylene terephthalate) resin layer is replaced by a mixed resin layer comprising the poly(ethylene terephthalate) resin and a specific resin, so that gas barrier properties can be markedly improved without lowering marked mechanical properties or lowering in transparency. Thus, it can be confirmed that the resulting body becomes a laminated plastic molded body in which a shelf life of a content which requires gas barrier properties can be markedly improved whereby the inventors have accomplished the present invention.
Accordingly, an object of the present invention is to provide laminated plastic molded bodies having extremely high gas barrier properties against oxygen and carbon dioxide gases, having excellent mechanical properties and having food hygiene properties.
To accomplish the above-mentioned objects, the present invention comprises the following constitution.
That is, the laminated plastic molded bodies of the present invention are laminated plastic molded bodies having a layered structure portion of three-layers or five-layers in which a resin layer A and a resin layer B are alternatively laminated, wherein the resin layer A provided at least at the surface side of the layered structure portion comprises a mixed resin layer of a poly(ethylene terephthalate) resin and at least one resin selected from the group consisting of an amorphous polyester resin, an ethylene naphthalate-ethylene terephthalate copolymer resin and a meta-xylene group-containing polyamide resin, and the resin layer B interposed between the resin layers A comprises a barrier resin layer comprising at least one resin selected from the group consisting of a meta-xylene group-containing polyamide resin and an ethylene-vinyl alcohol copolymer resin.
In the laminated plastic molded bodies having the above-mentioned constitution, the above-mentioned poly(ethylene terephthalate) resin preferably comprises a resin in which 80 mol % or more, preferably 90 mol % or more of a dicarboxylic acid component constituting the polymer is a terephthalic acid unit, and 80 mol % or more, preferably 90 mol % or more of a dialcohol component constituting the polymer is an ethylene glycol unit.
Moreover, the above-mentioned amorphous polyester resin is preferably an amorphous polyester resin obtained by copolymerizing at least one copolymer component selected from the group consisting of isophthalic acid, diphenyl ether 4,4-dicarboxylic acid, naphthalene-1,4-dicarboxylic acid, naphthalene-2,6-dicarboxylic acid, adipic acid, sebacic acid, decan-1,10-dicarboxylic acid, hexahydroterephthalic acid, propylene glycol, 1,4-butanediol, neopentyl glycol, diethylene glycol, 1,4-cyclohexanedimethanol, 2,2-bis(4-hydroxyphenyl)propane and 2,2-bis(4-hydroxyethoxyphenyl)propane, etc., in addition to terephthalic acid and ethylene glycol.
Incidentally, as the amorphous polyester resin, for example, a gas barrier polyester resin commercially available as Mitsui B-010 manufactured by Mitsui Kagaku Co., Ltd., or a polyester type gas barrier resin commercially available as RB8550 manufactured by Toyo Boseki Co., Ltd. can be used.
Moreover, it is preferred that the above-mentioned ethylene naphthalate-ethylene terephthalate copolymer resin is a copolymer resin comprising 5 to 45 mol % of an ethylene naphthalate unit and 95 to 55 mol % of an ethylene terephthalate unit. This is because, in these ranges, compatibility with the poly(ethylene terephthalate) resin becomes good and improvement in the barrier characteristics of the resin layer A by mixing said copolymer resin can be realized.
Furthermore, it is preferred that the above-mentioned meta-xylene group-containing polyamide resin is a polyamide resin comprising a polymer containing 70 mol % or more of an amide unit obtained from meta-xylylene diamine alone, or a mixed xylylenediamine containing meta-xylylenediamine and 30 mol % or less of para-xylylenediamine based on the total xylylenediamine and xcex1xc2x7xcfx89-aliphatic dicarboxylic acid having 6 to 10 carbon atoms.
Moreover, it is preferred that, in the resin forming the mixed resin layer, at least one resin selected from the group consisting of the amorphous polyester resin, ethylene naphthalate-ethylene terephthalate copolymer resin and meta-xylene group-containing polyamide resin is contained in an amount of 5 to 45% by weight. This is because, when the compounding amount is less than 5% by weight, improvement in barrier properties due to the mixed resin layer is not remarkable, while when it exceeds 45% by weight, moldability of said mixed resin layer becomes poor whereby unevenness in film thickness is liable to be caused and the molding step is liable to become unstable. From the same point of view, the compounding amount thereof is preferably 5 to 20% by weight.
Moreover, a weight of the resin forming the above-mentioned resin layer B is preferably 2 to 25% based on the weight of the resin forming the resin layer A and the resin layer B. This is because the meta-xylene group-containing polyamide resin or die ethylene-vinyl alcohol copolymer resin to be used for forming the resin layer B shows an excellent gas barrier properties by a single resin layer made of the resin, but the presence of the resin layer causes lowering in mechanical properties or lowering in transparency, so that these disadvantages can be avoided by decreasing the amount of these resins.
Also, it is preferred that the above-mentioned laminated plastics molded body is a container, and at least a body portion and a bottom portion of the above-mentioned container are constituted by the above-mentioned layered portion.
Moreover, the resin layer B provided by being interposed between the resin layers A comprises a barrier resin layer comprising at least one resin selected from the group consisting of a meta-xylene group-containing polyamide resin and an ethylene-vinyl alcohol copolymer resin. The meta-xylene group-containing polyamide resin is a generally used resin as a barrier resin. Preferred examples of the resin are the same as the meta-xylene group-containing polyamide resin to be used in the mixed resin layer constituting the above-mentioned resin layer A. On the other hand, the ethylene-vinyl alcohol copolymer resin is also generally used resin as a barrier resin. In the points of moldability and gas barrier properties, it is preferred to use an ethylene-vinyl alcohol copolymer resin containing 50 to 70 mol % of a vinyl alcohol unit.
As mentioned above, in the laminated plastic molded body of the present invention, by making the resin layer A a mixed resin layer of the poly(ethylene terephthalate) resin and a specific resin which is less worsen the moldability of the poly(ethylene terephthalate) resin and has high gas barrier properties and nontoxicity, and laminating it with the resin layer B, without accompanying marked lowering in mechanical properties or lowering in transparency, the gas barrier properties which are not affected by the circumferential atmosphere can be markedly improved when the molded body is a container, etc.
The laminated plastic molded body of the present invention can be molded by the same molding means as in the conventional molded body of a laminated plastic container comprising the poly(ethylene terephthalate) resin layer and the other thermoplastic gas barrier resin layer, i.e., by a direct blow molding, a parison blow molding or a biaxial drawing blow molding, etc. The biaxial drawing blow molding is preferred since more preferred mechanical properties can be obtained.